1. Field of the Invention
The present invention concerns a circular polarization antenna whose radiation pattern is in the shape of a body of revolution about an axis and has a radiation minimum in the direction of this axis.
2. Description of the Prior Art
Antennas of this type are usually implemented as a configuration of multirod conductors disposed in a tourniquet around the axis of the antenna, each rod being excited separately by a line from a distributor.
Such antennas are described, for example, by N.T. Lindeblad in Antennas and Transmission Lines at the Empire State Building Television Station, RCA Communications, Apr. 1941 (in which disclosure four dipoles are excited in phase separately, each by its own line), by M. S. Gatti and D. J. Nybakken in A Circularly Polarized Crossed Drooping Dipole Antenna, IEEE Antennas and Propagation Symposium Digest, 7-11 May 1990, Vol. 1, pp. 254-257, and by C. C. Kilgus in Shaped-Conical Radiation Pattern Performance of the Backfire Quadriflar helix, IEEE Transactions on Antennas and Propagation, May 1975 (in which disclosure four rods are excited by a power splitter and phase shifter system with respective phases of 0, 90, 180 and 270.degree.).
Antennas of this type are routinely used on satellites for telemetry and remote control links, for example, and on land and maritime mobiles, in particular for satellite communication and location systems.
Antennas of the aforementioned type can also be implemented in the form of slotted printed circuit antennas, but these require a complex matching circuit.
The principal drawbacks of these various prior art antennas are their complexity, their relative fragility and the high cost of the excitation system which is typically a four-channel system requiring the provision of power splitter, phase shifter and balancer devices.
One object of the present invention is to propose an antenna of the aforementioned type, that is to say a circular polarization antenna having a radiation pattern which is in the shape of a body of revolution about an axis with a radiation minimum on said axis (a more or less toroidal shape pattern, for example) but with a much simpler structure and a direct excitation system requiring no power splitter, phase shifter or balancer devices.
A subsidiary object of the present invention is to propose an antenna of this type in which the maximum radiation direction can be varied by a simple choice of parameters so that the same basic structure can without difficultly yield an entire family of antennas suited to the various applications envisaged.